This invention relates to miniature transducers and signal booster elements used in small computer disk drives.
Miniature transducers are known which are used in disk drives to write data to and read data from magnetic storage disks. One such miniature transducer type is a thin film magnetic transducer, which comprises a pair of pole pieces joined at a first region, usually termed the back gap region, and spaced at an opposing region, usually termed the pole tip region. In between the back gap region and the pole tip region, the pole pieces diverge in order to accommodate an electrical coil which is electrically insulated from the pole pieces. The coil is electrically connected to associated read/write circuitry. The transducer is typically fabricated on a relatively thick substrate, usually termed a slider, with the pole tip region terminating at a surface termed the air bearing surface (ABS). A typical example of such a transducer is described and illustrated in U.S. Pat. No. 4,458,279 and the additional references cited therein, the disclosures of which are hereby incorporated by reference.
Another miniature transducer type is termed a composite magnetic transducer, which is shown in co-pending, commonly assigned U.S. patent application Ser. No. 07/772,981 filed Oct. 7, 1991, the disclosure of which is hereby incorporated by reference. Essentially, a composite magnetic transducer comprises a two piece magnetic core element fabricated from a suitable material, such as ferrite, which is formed separately and then glass-bonded to a hard ceramic slider. The ferrite core element is bonded to the same surface as the support surface on which the thin film transducer is formed, the ferrite core being bonded to an ABS rail lobe or in a position intermediate the two spaced lobes. The ferrite core element has a gap which functions in a manner similar to the pole tip region of a thin film magnetic transducer, with the gap dimensions being defined by the glass bonding material and the process employed. An improvement over the composite head is termed the MIG head, which is an abbreviation for metal-in-gap. In this type of miniature transducer, a thin film of metal (typically Fe-Al-Si) is provided in the gap on the gap confronting surface of the downstream ferrite core piece. This arrangement provides for improved performance in general. Two typical examples of MIG heads are described and illustrated in the publication entitled "Recording Characteristics of MIG Heads", Shinohara, et al., IEEE Transactions on Magnetics, Vol. 24, No. 6, November, 1988, pages 2626-2628, and the additional references cited therein, the disclosures of which are hereby incorporated by reference. In all such composite heads, the ferrite core has an aperture, and a multi-turn coil of wire is wound about the core through the aperture, the coil being electrically connected to the associated read/write circuitry.
The demand for increasing data density on magnetic media has led to the requirement for substantially smaller track widths and transducers with correspondingly smaller gap dimensions. With decreasing gap size, the amplitude of the signal output by the transducer coil is corresponding reduced. This is undesirable, since noise signals increasingly mask the data signals generated by the coils during a read operation, which leads to erroneous data retrieval. In the past, attempts have been made to compensate for this decrease in signal amplitude by adding more turns to a transducer coil. For thin film transducers this solution is less than desirable, however, since it leads to an increased thickness of the transducer: in particular, in order to accommodate more turns, the coil is fabricated in several layers. This increased thickness of the transducer is highly undesirable because of a corresponding increase in noise, resistance and power consumption. Moreover, additional process steps are required, which increase production cycle time and decrease the yield rate, thereby contributing to higher cost per unit. For composite transducers, the additional turns solution is less feasible, since the coil is composed of individual turns of a continuous wire which cannot be decreased in diameter without sacrificing tensile strength, which leads to greater difficulty in fabricating such transducers and a lower manufacturing yield.
An improvement in the signal amplitude generated by such miniature transducers has been afforded by the use of a miniature thin film transformer to boost the electrical signal output from the thin film transducer. In our U.S. Pat. No. 5,072,324, issued Dec. 10, 1991 for Thin Film Transducer/Transformer Assembly, the disclosure of which is hereby incorporated by reference, a suitable thin film transformer is described which is formed on one of the two slider lobes in the position normally occupied by one of the thin film transducers in the prior art devices. This thin film transformer includes a bottom pole member, a top pole member forming a closed magnetic path with the bottom pole member, and a coil. The top and bottom pole members are fabricated of a magnetically permeable material. The electrically conductive coil is positioned between the top and bottom pole members, the coil having a pair of ends and a tap connection between the ends. The bottom pole member of the transformer includes first and second end portions and an intermediate body portion extending therebetween. The top pole member includes first and second end portions and an intermediate body portion extending therebetween and disposed above the intermediate body portion of the bottom pole member to provide an interior space for accommodating the coil, and the first and second end portions of the bottom pole member are coupled to the first and second portions of the top member, respectively. In addition to being located on one of the two lobes, the transformer can also be positioned elsewhere on the same substrate as the thin film transducer, or can be formed as a separate unit. The transformer coil is electrically connected to the transducer coil and to the follow on electrical circuitry by means of conductive leads. Like the transducer, the thin film transformer is fabricated using integrated circuit fabrication techniques.
The above-referenced co-pending U.S. patent application Ser. No. 07/772,981 discloses a further extension of the invention disclosed and claimed in the U.S. Pat. No. 5,072,324 by substituting a discrete booster element for the monolithically formed thin film transformer, the signal booster element having a pair of input terminals and a pair of output terminals. A coupling means is provided which includes a first conductive path coupled between one of the transducer coil ends and one of the signal booster element input terminals, and a second conductive path coupled between the other one of the transducer coil ends and the other signal booster element input terminal. The output signals from the transducer/signal booster assembly are taken from the output terminal of the signal booster element. The signal booster element may comprise a thin film transformer as described in the above-referenced '324 patent or an integrated circuit amplifier. In either form, the signal booster element serves to boost the amplitude of the signal generated by the transducer coil, with the amount of amplitude boost being dependent upon the turns ratio of the two portions of the transformer or the gain of the amplifier. The transducer and the signal booster element are supported by the substrate/slider in closely adjacent fashion, either on the same surface or on different surfaces. Each of these two major elements may be formed either independently or (in the case of the thin film transducer and transformer or integrated circuit amplifier embodiments) concurrently.
While the above describe signal amplitude arrangements provide improved performance for miniature transducers in small computer disk drives, these arrangements can only be applied to existing transducer/slider designs by changing the manufacturing process, which is not always economical to do for well established designs. Consequently, the need exists for a signal booster which is directly compatible with existing transducer designs, amenable to use with future designs and which is relatively inexpensive to implement.